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Abstract

We present dynamically reconfigurable photonic crystal nanobeam cavities, operating at ~1550 nm, that can be continuously and reversibly tuned over a 9.5 nm wavelength range. The devices are formed by two coupled nanobeam cavities, and the tuning is achieved by varying the lateral gap between the nanobeams. An electrostatic force, obtained by applying bias voltages directly to the nanobeams, is used to control the spacing between the nanobeams, which in turn results in tuning of the cavity resonance. The observed tuning trends were confirmed through simulations that modeled the electrostatic actuation as well as the optical resonances in our reconfigurable geometries.

Figures (3)

Coupled photonic crystal nanobeam cavities. a, SEM image of a representative fabricated structure. The suspended silicon is in contact with gold electrodes seen at the edge of the image and is supported by islands of SiO2 (scalebar = 1 μm). b, SEM image showing the deflection of the nanobeams due to electrostatic actuation. c, Finite element simulations showing nanobeams deflected due to an applied potential. The insets depict the Ey component of the optical supermodes of the coupled cavities. d, Simulation data: the red curve shows the lateral separation of a pair of nanobeams, measured at the center of the structure, as a potential is applied across them, while the blue curve shows the force generated due to the applied voltage.

Electrostatic tuning of a coupled photonic crystal nanobeam cavity. a, Finite element simulations showing the dependence of the even (shown in red) and odd (blue) supermode resonance on the applied bias voltage. b, Experimental data showing the measured resonances for even and odd supermodes. The trend seen in the experimental data matches well with the simulated results. The slight discrepancy in the absolute value of resonant wavelength can be attributed to uncertainty in the thickness and refractive index of the device layer of the SOI wafer, as well as the amount of tensile stress in the nanobeams. c Detected spectrum and Fano fits [26] at different applied voltages.

(Media 1) Sensitivity of the coupled-cavity resonance and the visualization of nanobeam deflection due to applied voltage. a, Experimental results showing the resonant wavelength of the even supermode as the bias voltage is stepped up to 6 V (red curve). Tuning up to 9.6nm is obtained in this cavity. The blue curve shows the sensitivity of the same cavity resonance to the applied voltage. A high sensitivity of 50 nm/V is obtained when cavity is operated around with a bias 6 V. The results are obtained for a cavity with initial (V = 0) nanobeam separation of -70 nm. b, Scanning electron microscopy images showing deflection of a pair of nanobeams under different bias voltages. The lower nanobeam remains grounded, while the potential on the upper nanobeam is increased as indicated.